In recent years, it has been desired to impart antibacterial power not only to the products such as medical supplies and containers used under high-temperature and high-humidity conditions like in kitchen, bathroom, washroom, etc., where bacteria and molds tend to easily propagate but also to articles used in public places such as straps and the like, materials related to dwelling, such as wallpapers and building materials, filters such as of air conditioners, and various other products such as stationeries. Therefore, a variety of antibacterial compositions have been proposed to meet the demand.
The antibacterial compositions have been provided in a variety of forms such as a formed body obtained by containing an antibacterial agent in a thermoplastic resin or a thermosetting resin, a film obtained by containing an antibacterial material in a coating material, and a dispersion solution obtained by dispersing an antibacterial agent in a solvent.
For instance, a patent document 1 listed below is describing a composition that contains a solvent, silver nanoparticles and a stabilizer. It is, however, difficult to disperse the silver nanoparticles without permitting them to be aggregated and, besides, a stabilizer is necessary to prevent the aggregation. Moreover, the above composition is not still satisfactory from the standpoint of transparency and efficient use of silver. A composition described in a patent document 2 is not the one that is to be applied onto an article that has been formed in advance unlike that of the patent document 1. Namely, the composition of the patent document 2 is used in combination with a resin to impart antibacterial power to a resinous formed article itself, and offers advantage in regard to productivity and sustenance of the effect. The composition, however, is not still satisfactory in regard to attaining more antibacterial power than the conventional antibacterial power using expensive substances such as silver and the like in amounts less than the amounts used so far.
A patent document 3 listed below describes a photocurable composition for antibacterial coating comprising a photocurable acrylic resin that contains a silver salt, and a patent document 4 listed below proposes a resinous formed body such as a protector board for use with various display devices, the resinous formed body comprising a photocurable resin that contains an antibacterial agent and/or an anti-molding agent so as to produce antibacterial power.
In a resin composition obtained by blending a photocurable acrylic resin with a silver salt like the resin compositions of the patent documents 3 and 4, it is difficult to efficiently and homogeneously disperse the silver salt in the acrylic resin, and it is not possible to obtain a resin composition satisfying both the requirements of antibacterial power and economy. It has, therefore, been desired to contain ultrafine silver particles capable of exhibiting excellent antibacterial power in the resin composition without permitting them to be aggregated.
Under such circumstances, the present inventors have proposed a transparent dispersion solution containing ultrafine silver particles formed of fatty acid silver and saccharin and a method of producing the same (JP-A-2013-241643). According to this method, ultrafine silver particles having excellent antibacterial power can be dispersed, by a relatively simple operation, in a low-boiling solvent that can be preferably used for imparting antibacterial power to the resin compositions without permitting the ultrafine particles to be aggregated in the low-boiling solvent. Further, the method efficiently removes by-products that affect the transparency of the dispersion solution. The obtained solution contains ultrafine silver particles without aggregation thereof, and exhibits excellent antibacterial power as well as excellent transparency.